In a 5-l. three-necked, round-bottomed flask fitted with an efficient stirrer(Note 1), a separatory funnel, and a thermometer in a well is placed a solution of 500 g. (9.7 moles) of powdered 95 per cent sodium cyanide in 1.2 l. of water and 900 cc. (713 g., 12.3 moles) of acetone. The flask is surrounded by an ice bath, and the solution is stirred vigorously. When the temperature falls to 15°, 2.1 l. (8.5 moles) of 40 per cent sulfuric acid(Note 2) is added over a period of three hours, the temperature being kept between 10° and 20°. After all the acid has been added the stirring is continued for fifteen minutes and then the flask is set aside for the salt to settle. Usually a layer of acetone cyanohydrin forms and is decanted and separated from the aqueous layer. The sodium bisulfate is removed by filtration and washed with three 50-cc. portions of acetone. The combined filtrate and acetone washings are added to the aqueous solution, which is then extracted three times with 250-cc. portions of ether(Note 3). The extracts are combined with the cyanohydrin previously separated and dried with anhydrous sodium sulfate. The ether and acetone are removed by distillation from a water bath, and the residue is distilled under reduced pressure. The low-boiling portion is discarded, and acetone cyanohydrin is collected at 78–82°/15 mm. The yield is 640–650 g. (77–78 per cent of the theoretical amount) (Note 4).

2. Notes

1.
It is advantageous to use a heavy metal stirrer because of the increased viscosity of the mixture toward the end of the reaction. Since some hydrogen cyanide may escape from the reaction mixture, the stopper carrying the stirrer should be fitted with a tube for leading off the gas or the reaction should be carried out under a hood.

3.
Extraction and distillation should be started as soon as possible after the completion of the reaction, and the distillation should be done as rapidly as possible to avoid decomposition.

4.
The preparation of acetone cyanohydrin from potassium cyanide and the bisulfite addition product of acetone is described in Org. Syn. 20, 43. The procedure given there furnishes a less pure cyanohydrin which, however, is suitable for some synthetic uses.

3. Discussion

Acetone cyanohydrin has been prepared from acetone and anhydrous hydrogen cyanide in the presence of a basic catalyst such as potassium carbonate, potassium hydroxide, or potassium cyanide;1 by the reaction of potassium cyanide on the sodium bisulfite addition product of acetone;2 and by the action of hydrogen cyanide, prepared directly in the reaction mixture, on an aqueous solution of acetone.3 More modern industrial procedures employ acetone, liquid hydrogen cyanide, and a basic catalyst.4

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